It is the usual practice, when refining many molten metals to add materials, including an air or oxygen blast, to cause reactions which form reaction products with elements which are not desired in the refined metal. Such reaction products will often physically separate from the desired refined molten metal, allowing those products, and the metal, to be poured separately from a vessel in which the refining reactions have occurred.
For example, A. K. Biswas and W. G. Davenport, in Extractive Metallurgy of Copper, 2d ed. (1980), available from Pergamon International Library, discuss in detail the converting of copper matte to crude or blister copper which is from 98.5 to 99.5 percent copper. Molten matte may contain a concentration of copper as low as thirty to thirty-five percent. It may also contain iron, sulphur, up to three percent dissolved oxygen, and an assortment of minor amounts of impurity metals, found in the original ore concentrate, but not removed during the smelting process.
This molten matte, charged at approximately 1100.degree. C. into a converter, is oxidized by an air blast, to remove the above-mentioned impurities. The reactions accompanying the refinement are exothermic, raising the temperature of the molten material. In a first slag-forming stage FeS is oxidized to FeO, Fe.sub.3 O.sub.4 and SO.sub.2 gas. Silica flux is added to combine with the FeO and a portion of the Fe.sub.3 O.sub.4 to form a liquid slag which floats on top of the molten matte and is poured off at several times during this first stage. Additional matte is added to the converter at intervals, followed by oxidation of a great portion of the FeS in that charge, and pouring off of the slag. When a sufficient amount of copper, in the form of matte is present in the converter, and the matte contains less than one percent FeS, a final slag layer is poured off, and the remaining impure copper is oxidized to blister copper.
Two types of converters have been used in the prior art. They are the Peirce-Smith converter and the Hoboken converter. Both have reactions vessels, or bodies, which are horizontally disposed cylinders.
The Peirce-Smith converter is discussed at page 179 of the reference cited above and includes one opening. The opening is used in connection with filling the converter, exhausting large volumes of SO.sub.2 bearing gas which are generated during the blowing operation and collected by means of a loose-fitting hood above the body, and pouring molten metal from the converter. For pouring purposes, the vessel is mounted on running wheels so that it may be turned about its longitudinal axis until the opening is disposed below the level of the molten metal to permit it to flow out. The Hoboken converter is shown at page 198 of the above-cited reference and includes a mouth for filling and emptying and a separate opening at the right hand end for escaping fumes. This opening is disposed axially of the converter and between it and the molten metal is a dam structure designated in the drawing on page 198 as a goose neck.
With the Peirce-Smith converter, it is difficult to create a good seal at the single opening because of the pouring of the metal from the opening when emptying the converter. This metal creates a deposit and otherwise deteriorates the opening so that it is difficult to assure that the hood for escaping exhaust will properly seal against the opening. A good seal is desirable to prevent noxious gases from escaping, and to prevent the dilution of the SO.sub.2 component by air, which is undesirable when the SO.sub.2 is used to produce sulfuric acid in an auxiliary process.
The problem of the Peirce-Smith converter is somewhat eliminated by the Hoboken converter. The goose neck is spaced to permit only gases to flow over the dam out the exhaust opening. This is rather a complicated, expensive structure, however, and during turning of the converter, liquid metal may reach the exhaust opening and cause deterioration of it and its associated structures. In addition, the presence of the dam decreases the capacity of the reaction vessel.